1. Field of the Invention
This invention relates to an improved process for the continuous production of fatty alcohols by the continuous hydrogenation of naturally occurring fats, oils and fatty derivatives. More specifically, the present invention relates to a process for the continuous hydrogenation of fatty acid esters to saturated or unsaturated fatty alcohols in a fixed-bed reactor in the presence of at least stoichiometric amount of hydrogen wherein unreacted hydrogen is recycled without reheating by means of a recirculation pump after separation from the liquid product.
2. Description of the Related Art
In the known process, the starting material, for example fatty acid methyl ester, is delivered by high-pressure pumps into the installation where it is mixed with compressed hydrogen, heated with the compressed hydrogen to the reaction temperature and introduced into the reactor from above. In addition to the ester group, carbon double bonds are also hydrogenated on the copper-containing catalyst so that, even where unsaturated esters are used, only saturated fatty alcohols are formed. In cases where a copper-free catalyst, on which the ester bond is selectively hydrogenated, is used, unsaturated fatty alcohols are formed from unsaturated fatty acid esters or glycerides.
After passing through the reactors, the reaction mixture is cooled and separated in a separator into the liquid phase and the gas phase. The liquid phase is vented and delivered to the methanol separation stage while the gas phase, which consists mainly of hydrogen, is circulated via a compressor.
In the methanol separation stage consisting of an evaporator, the fatty alcohol is freed from the methanol and may then be used without further purification.
The invention also encompasses the direct catalytic hydrogenation of glyceride oils to fatty alcohol and propane-1,2-diol and of fatty acids to fatty alcohol, as described for example in U.S. Pat. Nos. 4,982,020; 4,855,273; and 4,935,556, the entire contents of each of which is incorporated herein by reference.
The known processes are characterized by a high excess of hydrogen, typically of the order of 100 to 200 moles of hydrogen per mole of ester. The large volume of gas which is circulated involves considerable outlay on equipment, more particularly for cooling and reheating, which is normally carried out in several stages. After leaving the reactor, the gas/liquid mixture passes through the heat exchanger used to preheat the starting material. This is followed by cooling with water. After separation of the liquid phase, the recycle gas is delivered together with fresh hydrogen into the feed line for fatty acid methyl ester by a gas circulation pump, is mixed with fatty acid methyl ester and the resulting mixture is preheated in the heat exchanger mentioned. Finally, the mixture passes through a peak heater.
The problem addressed by the present invention was to reduce the outlay on equipment for cooling and reheating the unreacted recycle gas involved in the process mentioned at the beginning without any reduction in the quality of the fatty alcohol produced.
The solution to this problem is realized by returning the unreacted recycle gas the reactor entrance without reheating and carrying out the hydrogenation reaction at a pressure of at least 200 bar and, more particularly, at least 250 bar.
Other than in the claims and in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term xe2x80x9caboutxe2x80x9d.
A process for the continuous production of a saturated or unsaturated fatty alcohol by hydrogenation of a fatty acid, a naturally occurring fat, or a fatty acid derivative been discovered. The process comprises contacting a fatty acid or fatty acid derivative with at least a stoichiometric amount of hydrogen at a pressure of from about 50 to about 300 bar and at a temperature of from about 160 to about 320xc2x0 C. in the presence of a catalyst to form a liquid product phase comprised of at least a fatty alcohol having the same number of carbon atoms as the fatty acid, a naturally occurring fat, or a fatty acid derivative and unreacted hydrogen. The unreacted hydrogen is then separated from the liquid product phase and is recycled to the beginning of the process without reheating. Because the hydrogen is recycled without further heating, the process economics are considerably improved without sacrificing the quality of the fatty alcohol produced by the process.